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You have the following codes?
P0300 = Random misfire detected. The engine is misfiring
P0302 = Cylinder # XXXXX misfire detected. Cylinder # XXXXX was first detected.
P0420 = Main catalyst below threshold (bank 1) . Catalytic converter is working lean.
Possible causes are insufficient fuel getting into the system..
1, Faulty O2 sensor.
2. Clogged fuel filter.
3. Vacumn leakages. Check for dislodged vacumn hoses, faulty PCV.
4. Faulty spark plugs.
What can I do to fix these problems?
Check the fuel filter first, if it is clogged, replace it.
Check the spark plugs as well.
For vacumn leakages, check all the hoses to see if any is broken or dislodged.